1. Field of the Invention
The present invention relates to a liquid crystal display device and a method of manufacturing the same and, particularly, to a fringe-field switching mode liquid crystal display device and a method of manufacturing the same.
2. Description of Related Art
A fringe-field switching (FFS) mode of a liquid crystal display device is a display technique that displays an image by applying a fringe electric field to liquid crystals filled between substrates placed opposite to each other. Because a pixel electrode and a counter electrode are formed by transparent conductive layers in the FFS mode liquid crystal display device, it is possible to obtain a higher aperture ratio and transmittance compared to an in-plane switching (IPS) mode.
In liquid crystal display devices, viewing angle characteristics are degraded due to the occurrence of a phenomenon called color shift that an image looks yellowish or bluish depending on the angle of view, tone reversal or the like. Thus, the FFS mode liquid crystal display device has the structure as shown in FIG. 8 so as to suppress the color shift and the tone reversal and thereby improve the viewing angle characteristics. Referring to FIG. 8, in the FFS mode liquid crystal display device according to related art, molecules of liquid crystals 20 are oriented perpendicular to or in parallel with a gate line 43. Further, a common electrode 8 placed opposite to a pixel electrode 6 with an insulating layer interposed therebetween has slits at an angle of ±1 to 20° with respect to the orientation axis (slow axis) of the liquid crystals 20, which are symmetric about the center of a pixel. In this structure, the orientation of the liquid crystals 20 changes as indicated by the dotted line in FIG. 8 when a voltage is applied, so that the liquid crystals 20 operate symmetrically in one pixel. This prevents the birefringence effect of the liquid crystals 20 from varying depending on the oblique angle of view, thereby improving the viewing angle characteristics.
In this structure, as shown in FIG. 9, it is necessary that the absorption axis of a polarizing plate on the array substrate side is at 0° or 90° and the absorption axis of a polarizing plate on the counter substrate side is at 90° or 0°, each with respect to the orientation axis (slow axis) of the liquid crystals 20, so that they are in crossed Nichols arrangement. In this arrangement, the polarization direction (optical axis) of transmitted light that is transmitted from the FFS mode liquid crystal display device is at 0° or 90° with respect to the gate line 43.
In the case of using a liquid crystal display device outdoors, a user may watch an image through polarized sunglasses. The absorption axis of the polarized sunglasses is oriented horizontally in order to prevent reflected light from entering the eyes. Accordingly, if transmitted light from the liquid crystal display device is in the horizontal direction, the polarized sunglasses absorb the light, and a user cannot view a displayed image. Therefore, when looking at an image through the polarized sunglasses, display looks all black in either horizontal (landscape) or vertical (portrait) position.
In order to address the above concern, a technique of attaching a λ/4 plate on top of the polarizing plate is disclosed in Japanese Unexamined Patent Publication No. 10-10523. Further, a technique of attaching a polarization canceling plate that combines two quartz plates on top of the polarizing plate to thereby improve the visibility when looking at images through polarized sunglasses is disclosed in Japanese Unexamined Patent Publication No. 10-10522. Furthermore, a technique of specifying the polarization direction of the polarizing plate on the display surface side to thereby improve the visibility when looking at images through polarized sunglasses is disclosed in Japanese Unexamined Patent Publication No. 10-49082.
However, because the techniques disclosed in Japanese Unexamined Patent Publications Nos. 10-10523 and 10-10522 require an additional member such as the λ/4 plate or the polarization canceling plate, the costs increase. Further, if such a member is attached to a liquid crystal display device, the thickness of the liquid crystal display device increases. On the other hand, if the technique disclosed in Japanese Unexamined Patent Publication No. 10-49082 is used in an FFS mode liquid crystal display device, the contrast decreases.
In light of the foregoing, it is desirable to provide an FFS mode liquid crystal display device with high display quality that enables a display to be viewed in both landscape and portrait positions through polarized sunglasses without need of any additional member, and a method of manufacturing the same.